1975 6hp siezed on the river today.....help!

smallieback

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Apr 19, 2015
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Went out to the Shenandoah today with the old lady on a used boat I picked up this winter. I had replaced the water pump gasket and lower unit spaghetti seal in February and changed the lower unit gear oil. It ran like a champ with the muffs on at the house yesterday so I thought we were good to go. Not two minutes after taking off up river the motor putted down to a stop. I went to pull the string again and it wouldn't budge an inch. Luckily I had just got a bow mounted trolling motor so the day wasn't completely ruined. After the trip was over and we were back at the house I put the motor in neutral and was able to spin the prop. I could pull the string but it was extremely resistant. So I waited for another hour and took the cowling off and was able to turn the flywheel by hand. I checked the spark plugs and took the cylinder head off. The pistons look good but I could see marks on the cylinder from the seizure. Im guessing the motor had seized but not enough to completely ruin the engine. My question is could this be caused by a wrong fuel to oil mix ratio or is it a cooling issue? Thanks for reading and any input is appreciated
 

racerone

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Dec 28, 2013
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36,047
Gas and oil is to be mixed at 50:1 on that motor.----------You did not install a new impeller when you replaced the water pump gasket ??????--------Did you check the thermostat ???/-----------The marks in the cylinders may mean that it needs an overhaul now.
 

nwcove

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May 16, 2011
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it could be you mixed the fuel wrong, or a cooling issue.....is the cyl head discolored? those motors are tough and you could be lucky , but i doubt it. if it was starved of oil, its parts or a somewhat costly project. i do need to ask.....what muffs did you run it with ??
 

smallieback

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Apr 19, 2015
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When I replaced the gasket I checked the impeller and it looked brand new so I didn't mess with it. the gasket though looked rough. it had the upgraded '79 water pump on it. the muffs I used were the round kind that came with the boat. I didn't buy them and don't know the brand but they're about 4 inches in diameter. the cylinder head looks good. there was a tiny bit of oil opposite where the plugs screw in. the plugs were dry and have a tan tint to them. I will upload pics if they will be any help. this is my first outboard and am wondering how to tell if the water pump and impeller are working?
 

175se

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Mar 6, 2014
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274
If I had to guess it would be cooling related, muffs will not work on that motor. Probably need to replace the water pump, running it on what you may have thought were muffs were not doing the pump any good. That motor has to be in a tank (or bucket) with the water at least half the way to powerhead.
 

Chinewalker

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Aug 19, 2001
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Is the thermostat in place? It's located under the cover on the cylinder head.
 

smallieback

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Apr 19, 2015
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Yes the thermostat is there and it works. Checked it today with a pot of water. I got in touch with LeeRoy from leeroysramblings and he pointed me in the cooling direction also. I fired the motor up in a 55 gallon trash can and took the thermostat cover off. There was no water being pumped up so I cut off the motor so it wouldn't over heat again. I dropped the lower unit and check the impeller etc. the intake screen is free and clear of any blockage. I noticed on the impeller that in the center of it where the brass ring is there is a square notch...is something supposed to be on the shaft that the impeller goes around to turn the impeller?
 

smallieback

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Apr 19, 2015
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the water level was about 4 inches above where the lower unit joins the upper...was that high enough 175se?
 

jbcurt00

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Oct 25, 2011
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If there is a key way in the impeller shaft and in the center of the impeller, yep its supposed to have a key in there to drive the impeller. On muffs there .may have been enough water pressure to spin the impeller or force water up into the motor. In a barrel or under way there isnt enough water pressure to do that.....
 

dazk14

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Jul 22, 2008
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966
If there is a key way in the impeller shaft and in the center of the impeller, yep its supposed to have a key in there to drive the impeller. On muffs there .may have been enough water pressure to spin the impeller or force water up into the motor. In a barrel or under way there isnt enough water pressure to do that.....

As stated above, you have found the problem. You might find the missing part on the shop floor where you originally took apart the water pump.
 

smallieback

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Apr 19, 2015
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ok so I dropped the lower unit slid off the impeller and housing and found no impeller drive pin....I looked on the shaft and saw what was left of one stuck in the hole....I tapped the back of the shaft and about 3/16" round pin fell out....what could've caused the head to shear off like that? thanks you guys for pointing me in the right direction
 
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